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Millions of people around the world have no access to sanitation that offers a “clean” solution. Therefore, Eawag is researching technical possibilities for treating wastewater and recovering resources from it. The main focus is on sustainable solutions for the southern hemisphere.

For example, faecal sludge can be dried and pressed into odourless pellets that can be burned like wood pellets. (Photos: Basil Stücheli/ETH Board)

This story can be told in two ways. First, there’s the market story. What a waste! All the valuable stuff in human excrement just poured down the sewers. Out of sight, out of mind. Money just thrown away...flushed away. But the public health story sounds very different. Housing developments need a fully functioning sewage system, otherwise hygiene emergencies are inevitable. Western countries have devel-oped centralised sewage systems over time, which work in this country but which also create costs. This approach doesn’t really work for cities in the southern hemisphere; the plants usually fail sooner or later, and the money invested goes down the drain. Decentralised systems are much better suited to collecting and treating sewage locally. But then the most important question arises: what to do with it? Not simply dumping it in the next stream, that’s for sure, but treating and burning would be the more hygienic solution, for example.

It gets really interesting when you bring the two stories together. This is the goal of research conductedby Linda Strande and Christoph Lüthi from Eawag.Both work in the Department of Sanitation and Water for Development (Sandec) and develop scenarios to establish wastewater management worthy of the name in the southern hemisphere. The focus is on people’s health, while resource recovery and “management” are the economic driving forces. Lüthi says that previous attempts to improve the waste-water situation in the southern hemisphere have largely ignored the economic aspects. This is the decisive factor when it comes to a sustainable and financially viable solution. Because the sewage system is not subsidised – there are simply no funds available for this – solutions must be sought that pay for themselves.

Linda Strande (Left) and Christoph Lüthi, both from the Department of Sanitation and Water for Development at Eawag

After years of research, the specialists from Dübendorf have indeed put together a series of economically impressive solutions: energy, nutrients for fer-tilisers and even animal feed can be obtained from waste water and faecal sludge. Almost all the nutrients come from the urine. A high-tech plant is in operation at Eawag itself, which separates the urinein the toilets and then processes it into valuable liquid fertiliser. Researchers are proud to report that Switzerland has recently even officially permitted the use of this fertiliser for food crops. However, less complex and more robust solutions for faecal sludge may prove to be much more interesting for cities in developing countries. That’s Strande’s area of specialisation. She has overseen various projects, for example in Uganda,which have demonstrated the practicability of the procedures. For example, faecal sludge can be dried and pressed into odourless pellets that can be burned like wood pellets, thus solving the problem of possible pathogens. The economic prospects are excellent, says Strande, and local industries have also shown great interest in the cheap pellets, provided they are produced in sufficient quantities.

The latest trick of the researchers is even more amazing: transforming animal or human waste into valuable protein. They use the larvae of the Black Soldier Fly (or BSF for short), which clean up pretty much all organic waste, be it salad leftovers, meat or food already digested by us. If this food mash is properly treated, hardly anything remains after the feast apart from fat larvae, which can be processed into food for farm animals or used in fish farming, for example.

"The economic prospects for pellets that can be used as fuel are excellent.”
Linda Strande, Department of Sanitation and Water for Development at Eawag

The potential is huge. On the one hand, there is the growing demand for these sorts of feed materials, economic pellets or nutrient-rich fertilisers. On the other hand, there is the appalling reality for about one third of the world’s population: sanitation for around 2.7 billion people is still provided decentrally without a sewer system or regulated wastewater dis-posal. Lüthi stresses once again that only solutions based on a market analysis will be viable on a broad scale. He doesn’t want to see any more “white elephants” – he’d prefer to see lots of black soldier flies